Method of making halocarbon polymers



Patented Aug. 14, 1951 METHOD OF MAKING HALOCARBON POLYMERS William T.Miller, Ithaca, N. Y assignor to the United States of America asrepresented by the United States Atomic Energy-Commission No Drawing.Application May 21, 1948, Serial No. 28,520

9 Claims. (Cl. 260-921) This application is a continuation-in-part of myapplication Serial No. 730,176, filed February This invention relates toa method of making polymers consisting essentially of carbon and halogenwith a high fluorine content, and more particularly to a method ofmaking polytrifluoromonochloroethylene and polydifluorodichloroethylene.

Polymers consisting substantially completely of carbon and halogen andcontaining a high pro-- portion of fluorine, because of their highchemical inertness have recently come to be of considerable interest inconnection with the handling of corrosive substances.

One object of the invention is to provide a method of making polymersconsisting essentially of carbon and halogen with a high percentage offluorine, that are of relatively high molecular weight.

Another object of the invention is to provide a method of making suchpolymers that is convenient, safe and inexpensive.

Still another object of the invention is to devise amethod of makingsuchpolymers which further are substantially free from hydrogen groups.

Other objects will appear hereinafter.

According to the invention, these objects may be accomplished by heatinga compound selected from the group of trifluoromonochloroethylene andthe difluorodichloroethylenes in the presence of elemental oxygen as a.polymerization promoter. A useful range of temperatures for carrying outthe process is about 40 C. to about 150 C. and a preferred range oftemperatures is about 60 C. to about 100 C. The polymerization issuitably carried out at atmospheric or elevated pressure. It ispreferable to have oxygen present in a concentration of 0.001%-0.4%based on the weight of the monomer, and better 0.001 %-0.05%.

' When oxygen is present in appreciably higher concentrations the yieldof polymer tends to decrease, apparently because of oxidation reactionswhich compete with the polymerization reaction. In accordance with thepresent invention oxygen -is used in a concentration such that itfunctions primarily as a polymerization promoter.

I have found that, in many instances, in polymerization processes inwhich relatively low temperatures are used polymers of relatively highmolecular weight tend to be produced, and that the converse of this istrue. Thus, for example,

and a compound of the formulaCzFo. On the other hand, in an applicationof myself jointly with Albert L. Dittman and Sherman K. Reed. Serial No.773,292, filed September 10, 1947, experiments are described in whichtrifluoromonochloroethylene is polymerized in the presence oftrichloroacetyl peroxide at temperatures of the order of C. and anexceedin y hi h molecular weight polymer, e. g., a plastic, is produced.The method of the present invention is useful when it is desired toproduce polymers consisting essentially of carbon and halogen with ahigh fluorine content that are of relatively high molecular weight. Ithas been found that it is feasible to polymerize the fluorochlorooleflnsmentioned by heating the olefin in the presence of oxygen at I havepassed tetrafluoroethylene continuously through a hot tube attemperatures of the order of 650 C. and have thereby produced the dimermoderately elevated temperatures; owing to the fact that the process iscarried out at moderate temperatures, polymers of relatively highmolecular weight are produced.

Another advantage of the present invention is that it is adapted to bulkpolymerization," that is, polymerization in the absence of a solvent orsuspension agent. Bulk polymerization is convenient because the polymerreadily separates from the monomer in which it is substantiallyinsoluble and thus recovery of the polymeric easily accomplished. Thepresent method is adapted to this procedure because at the moderatetemperatures used the reaction proceeds" at a moderate rate of speed andgood heat transfer is attained. Experiments have been carried out whichindicate that the mechanism of polymerization involves the formation ofan olefin peroxide in situ by combination of the oxygen with the olefin}fluorochloroolefins indicated is preferably car-- ried out bymaintaining the olefin in contact with elemental oxygen at a temperatureconducive to the formation of the olefin peroxide and unfavorable forits decomposition, e. g., at about -20 C. or below, to build up anappreciableizoncentration of the olefin peroxide in the olefin; andthereafter heating the olefin containing the peroxide at a temperaturewithin a range indifragments of the promoter may enter thepolymerchains. However, the presence of even a small percentage ofhydrogen in the polymeric product may appreciably decrease itsresistance to corrosive substances, particularly elemental fluorine. Inthe present method, on-the other hand, there is no means by whichhydrogen can be introduced.

Improved. processes have been developed in which the amount of hydrogenthat may be introduced into the polymer chains is substantially reducedor in which substantially no hydrogen is introduced. Thus, inapplication Serial No. 773,292 referred to above a process is disclosedof polymerizing an olefin such as trifluoromonochloroethylene in thepresence of a halogen substituted acetyl peroxide promoter, particularlya 'sisting"essentially of carbon. and halogen with a high fluorinecontent containing substantially no hydrogen can be produced and anolefin per.-

oxlde promoter can be formed in situ and directly used inthep'olymerization. The following examples illustrate the methodofthepr'esent invention. The no strength temperature (abbreviated N. S.T.) of the polymers y that are given were obtained in the mannerdescribed in my application Serial No. 730,176.

Emmple 1 189.3 gs. of trifluoromonochloroethylene which had beenpreviously'purifled by distillation from P205 and'then throughsilica-gel was pumped into a 300 cc. heavy wall Pyrex glass bomb at '78C. The bomb was cooled to -190 C. and 'was connected to a vacuum pump toempty it of gas. In order to introduce oxygen to serve as a promoter forthe polymerization, the open bomb was then'stored in the dark under puregaseous oxygen" for about 3 days at -78 C. The bomb was then sealed andplaced in a shaker in a dark place, after which the temperature wasraised to 70 C. and then maintained between 54 and 70 C..for 19 hours.About 24.6 gs. of polytrifiuoromonochloroethylene having a Fisher-Johnsmelting point range of 208-212 C. was recovered.

' Example 2 A- stainless steel container with a capacity of 2.61. wascharged with about 1650 gs. of trifluoromonochloroethylene that had beenpurified by distillation from P205. The container, cooled by means ofsolid carbon dioxide, was pumped until all the air was displaced byolefin vapor. Oxygen was then introduced into the container in an amountsuflicient to increase the pressure by 200 Hence special pre- 4 mms. Thecontainer was sealed and heated at 60-65 C. under agitation for about 44hours. About 71 gs. of a polymer having a Fisher-Johns melting point of206-207 C. was recovered.

The polymer thus produced was useful as a starting material for theproduction of-a valuable. highly stable lubricant .by my process ofthermal cracking.

Example 3 A 1-l. flaskwas evacuated and charged with 800 mls. liquidtrifiuoromonochloroethylene.

Oxygen was bubbled through the monomer for 10 minutes atabout -l8- C.and then an oxygen pressure of 1 inch of mercury greater thanatmospheric was maintained while the monomer was refluxed with acondenser cooled by solid carbon dioxide. Refluxing was carried onintermittently over a period of about 2 days; the monomer was refluxedfor a total of about 18 hours and in the intervals between reflux timesthe reaction mixture containedfin the' flask was kept in a Dewarapparatus containing solid carbon dioxide. In order to determine thepresence of a peroxide after this treatmenta sample' of the reactionmixture was tested by the following method. The sample was added toan-alcoholic solution of potassium iodide, acetic acid and sodiumacetate, the mixture was warmed and the liberated iodine was titratedwith a standard aqueous solution of sodium thiosulfate. By this method aperoxide was found to be present equivalentto about 0.035% oftrichloroacetyl peroxide. An-

other sample weighing about 44 gs. of the reaction v mixture was warmedand kept at a temperature between C. and C. for about 45 hours.

About 5 gs. of a solid polymer having a N. S. T.

of 220 0., representing recovered.

Example 4 About 26 gs. of asymetric difluorodichloroethylene (CF2=CC 12)maintained at'-78 C. was saturated with oxygen by bubbling oxygenthrough the liquid monomer. The reaction mixture was then heated atabout C. for about 48 hours; Approximately 0.7 gs. was recovered of apolymer with a very high softening point,- e'. g., it did not melt up to300 C., which indicated its usefulness as a plastic. 1

Thus, by means of the present invention, poly mers consistingessentially of carbon and halogenwith a high fluorine content thatMoresistant to corrosive substances such as acids. alkalies, thehalogens, etc. are produced, of relatively high molecular weights suchthat the polymers are useful as plastics or for the production oflubricating oils andgreasesby cracking; The process developed isconvenient, safe and'ineirpensive. The use of oxygen as a polymerizationpromoter is also advantageous for use with con tinuous flowpolymerization processes. Oxygen may be conveniently provided andmetered under high pressures either as a gas or in solution without theprecautions necessary to avoid decomposition of an organic peroxide; 3

Since many embodiments might be made of the present invention and sincemany changes might be made in the embodiment described, it is to beunderstood that the foregoing descrip= tion is to be interpreted asillustrative only and not in a limiting sense.

Iclaim:

'l. A method useful for producing polymers which soften above 200 C.which comprises heating an'olefin selected from the group of tria yieldof about 11%, was

fluoromonochloroethylene and difluorodichloroethylene at a temperaturein the range of 40 C. to 150 C. in the presence of elemental oxygen as apolymerization promoter to produce a solid polymer.

2. A method useful for producing polymers which soften above 200 C.which comprises heating an olefin selected from the group oftrifluoromonochloroethylene and difluorodichloroethylene at atemperature in the range of 60 C. to 100 C. in the presence of elementaloxygen as a polymerization promoter to produce a solid polymer andseparating the polymer so produced from the reaction products.

3. A method useful for producing polymers which soften above 200 C.which comprises heating an olefin selected from the group oftrifluoromonochloroethylene and difluorodichloroethylene at atemperature in the range of 40 C. to 150 C. in the presence of 0.001% to0.4% elemental oxygen to produce a solid polymer and separating thepolymer so produced from the reaction products.

4. A method useful for producing polymers which soften above 200 C.which comprises heating an olefin selected from the group oftrifluoromonochloroethylene and difiuorodichloroethylene at atemperature in the range of 40 C. to 150 C. in the presence of 0.001% to0.05% elemental oxygen to produce a solid polymer and separating thepolymer so produced from the reaction products.

5. A method useful for producing polymers which soften above 200 C.which comprises heating trifiuoromonochloroethylene at a temperature inthe range of 60 C. to 100 C. in the presence of 0.001% to 0.4% elementaloxygen to produce a solid polymer and separating the polymer so producedfrom the reaction products.

6. A method useful for producing polymers which soften above 200 C.which comprises heating asymetric difluorodichloroethylene at atemperature in the range of 60 C. to 100 C. in the presence of arelatively minor proportion of .elemental oxygen to produce a solidpolymer and separating the polymer so produced from the reactionproducts.

7. A method of making a polymer consisting essentially of carbon andhalogen with a high percentage of fluorine which .comprises maintainingtrifluoromonochloroethylene in contact with elemental oxygen at atemperature not higher than about 20 C. to produce the peroxide oftrifiuoromonochloroethylene in situ, and thereafter heating saidtrifiuoromonochloroethylene containing said peroxide at a temperature inthe range of C. to C. to produce a solid polymer and separating thepolymer so produced from the reaction products.

8. The method for making a polymer consisting essentially of carbon andhalogen with a high percentage. of fluorine which comprises maintainingan olefin selected from the group of trifluoromonochloroethylene anddifluorodichloroethylene in contact with elemental oxygen at atemperature not higher than about 20 C. to produce the peroxide of saidolefin in situ, and thereafter heating said olefin containing saidperoxide at a temperature in the range of 40 C. to C. to produce a solidpolymer and separating the polymer so produced from the reactionproducts.

9. A method useful for producing polymers which soften above 200 C.which comprises heating an olefin selected from the group oftrifluoromonochloroethylene and difiuorodichloroethylene at atemperature in the range of 60 C. to 100 C. under substantiallyanhydrous conditions in the presence of elemental oxygen as apolymerization promoter to produce a solid poly- WILLIAM T. MILLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,369,520 Barnes Feb. 13, 19452,394,243 Joyce Feb. 5, 1946 FOREIGN PATENTS Number Country Date 465,520Great Britain May 3, 1937 590,390 Great Britain July 16, 1947 OTHERREFERENCES Mfller et al.: Ind. Eng. Chem. 39, 333-337, March 1947.

1. A METHOD USEFUL FOR PRODUCING POLYMERS WHICH SOFTEN ABOVE 200* C.WHICH COMPRISES HEATING AN OLEFIN SELECTED FROM THR GROUP OFTRIFLUOROMONOCHLOROETHYLENE AND DIFLUORODICHLOROETHYLENE AT ATEMPERATURE IN THE RANGE OF 40* C. TO 150* C. IN THE PRESENCE OFELEMENTAL OXYGEN AS A POLYMERIZATION PROMOTER TO PRODUCE A SOLIDPOLYMER.